Multi-degree of freedom nonlinear energy sinks for passive control of vortex-induced vibrations in a sprung cylinder

The application of multi-degree of freedom nonlinear energy sinks (MDOF-NES) to control the vortex-induced vibrations of a sprung cylinder passively is investigated in this paper. The flow-induced loads on the cylinder are modeled by the wake Van der Pol oscillator. The MDOF-NES consists of three oscillators connected in series, where the first mass is linked to the cylinder structure by a linear spring. The second mass is connected with the first and third masses by pure cubic springs and linear viscous dampers. The cylinder-MDOF-NES assemble model is analyzed in two scenarios involving lower and strong linear stiffness couplings. Numerical investigations of the bifurcation and limit cycle oscillation (LCO) behavior associated with parametric changes are performed. An appropriate design of the MDOF-NES parameters allows mitigating the sub-critical behavior and control LCO amplitudes. The MDOF-NES approach based on the lower linear stiffness coupling has shown to be more effective in controlling the LCO amplitudes. Moreover, it is verified that the MDOF-NES masses have a significant effect on the LCO stability, amplitudes, and synchronization frequency range. Comparison between the MDOF-NES and a classical Type I NES was also performed to ensure the superiority of the MDOF-NES in suppressing the vortex-induced oscillations.